1. Field of the Invention
This invention relates to an orifice plate in which through-holes defining orifices or discharge ports for discharging the ink of a recording head mounted on an ink jet recording apparatus used in a copying machine, a facsimile apparatus, a word processor, a printer for the output of a computer, a printer for video output or the like and positioning apertures for effecting the positioning of the recording head in the recording apparatus are provided with good arrangement accuracy, and to an ink jet recording head using said orifice plate as well as to an ink jet recording apparatus carrying said head thereon.
2. Related Background Art
An ink jet recording apparatus adopts a method of discharging ink as recording liquid, forming flying liquid droplets and causing the ink to adhere to a recording medium such as paper to thereby accomplish recording. Systems for forming ink droplets in such ink jet recording apparatus include a system generally called the continuous type wherein pressurized ink is made into a liquid droplet stream by imparting vibrations thereto by a piezo-electric element. Charges are imparted to the liquid droplet stream by an electrode and only the necessary droplets are deflected to thereby accomplish recording. Also known is a system called the on-demand type which utilizes, for example, a pressure change in a liquid path caused by the deformation of a piezo-electric element, and a system which uses a heat generating element as an ink discharge energy generating member as in the system described in U.S. Pat. No. 4,723,129 (Endo et al.) or U.S. Pat. No. 4,740,796 (Endo et al.) wherein a heat generating element is provided in a liquid path, and ink is suddenly heated and a liquid droplet is discharged by the force of the resultant bubble.
Among the above-described ink jet recording systems, particularly the system using a heat generating element as a discharge energy generating member, there are advantages such as the ease with which orifices for discharging ink-forming ink droplets is made highly dense with good accuracy, and the possibility of high-speed recording.
On the other hand, as the typical printing systems in the ink jet recording apparatus, there are the serial types in which use is made of a recording head having orifices arranged in a spacing narrower than the width of an image to be recorded and the recording head is scanned relative to a recording medium such as paper to thereby accomplish recording line by line. In addition the full line type has orifices which are arranged in the main scanning direction, for example, over the full width of an image to be recorded, and a recording head and a recording medium are moved relative to each other in the sub-scanning direction to thereby record one line substantially at a time.
Of the above-described two printing systems, full line type printers are being actively developed from the viewpoint that they can sufficiently meet the desire for high-speed recording. Moreover, in this full line type printing system, a number of recording heads having orifices arranged therein are juxtaposed to constitute a recording apparatus, whereby it becomes possible to accomplish recording in a larger area at a time. Further, attention has been paid to this printing system from the viewpoint that by the use of recording heads in which the arrangement density of orifices is enhanced, for example, the requirement for high-speed recording of colored images of high density and high quality can be met easily.
However, in a recording head in which there are arranged a plurality of heads each having several tens to several hundreds or several thousands of discharge ports, particularly, full line type heads, the influence of the arrangement accuracy of all the orifices upon the image recording accuracy is particularly critical therefore, it is necessary to make not only the arrangement accuracy of the orifices influenced by the arrangement of the recording heads, but also the arrangement accuracy of the orifices influenced by the relative positional relationship among the plurality of recording heads sufficient.
Description will hereinafter be made of the case of a recording apparatus of the conventional construction as shown, for example, in U.S. Pat. No. 4,477,823 (Matsufuji et al.) or U.S. Pat. No. 4,499,478 (Matsufuji et al.) wherein four recording heads 1 of the full line type in each of which fourteen ink jet elements 1a shown in FIG. 1A of the accompanying drawings having a number of orifices (not shown) arranged at a predetermined density are arranged in staggered relationship and juxtaposed as shown in FIG. 1B of the accompanying drawings. According to our experiment, it has been found that when the positions of the orifices in the direction of arrangement thereof and the degree of parallelism of the recording heads 1 are taken into consideration, the arrangement accuracy of at least .+-.1/4 dot pitch (for example, .+-.30 .mu.m if the arrangement density of the orifices is 8 dot/mm, or .+-.15 .mu.m if said arrangement density is 16 dot/mm) is required in installing the recording heads 1.
However, the positioning of the recording heads in such an apparatus is accomplished by discretely attaching fixing jigs 2 and 3 to the body of each recording head 1 as shown in FIG. 1B, and providing positioning pins 4 and 5 at the locations of the recording apparatus whereat the recording heads 1 are installed.
More particularly, as shown in the enlarged perspective view of FIG. 1A, the degree of parallelism of all heads 1 and the arrangement accuracy (dimension A) of the orifices are determined by positioning holes 6 and 7 formed in the fixing jigs 2 and 3.
However, the fixing jigs 2, 3 and the positioning pins 4, 5 are made solely by machining, and for example, to obtain very precise arrangement accuracy of recording heads such as .+-.30 .mu.m or .+-.15 .mu.m as mentioned above, a high machining accuracy is required for making of these jigs and pins, and this has caused the cost of the recording heads to rise remarkably.
That is, in a recording apparatus having a plurality of recording heads of the conventional full line type, even if the recording head body has been made at no small cost by the use of a technique such as photolithography which enables fine working at high accuracy, it is the positioning method which is low in mass productivity and costly in working and assembling mechanical parts highly accurately that is inefficient and costly.
As a result of numerous experiments we have carried out repetitively, we have found that the above-noted problem of positioning also affects the quality of recorded images such as the ink discharge characteristic or the adherence of ink droplets to desired accurate locations on a recording medium. Further, as a result of experiments we have carried out, we have also found that the quality of images in not only the full line type heads but also the heads used in the serial system is affected by the above-described positioning of the discharge ports.